Chronic Kidney Disease (CKD) Animal Models: Types, Induction Methods, and Efficacy Endpoints

Chronic kidney disease (CKD) affects tens of millions of adults in the United States.^[S1] Nonclinical efficacy studies for CKD candidates depend on choosing an animal model whose pathology matches the mechanism being targeted. This article reviews the main rodent CKD models, how they are induced, which endpoints are used to evaluate efficacy, and what to consider when outsourcing these studies to a US contract research organization (CRO).

Overview of CKD models

Why CKD models are needed

CKD is the umbrella term for a sustained loss of kidney function. According to the Centers for Disease Control and Prevention (CDC), more than 1 in 10 US adults (14%, about 37 million people) are estimated to have CKD, and about 9 in 10 of them do not know it.^[S1] The cost falls heavily on Medicare: spending for beneficiaries aged 66 or older with CKD (not including kidney failure) was nearly $77 billion in 2021, about a quarter of Medicare spending in that age group, and total Medicare costs for people with end-stage renal disease reached $55.3 billion in 2023, according to the United States Renal Data System (USRDS) Annual Data Report.^[S2][S17] Slowing CKD progression before kidney failure is the objective that CKD drug development programs address.

Demand for new agents that slow CKD progression or improve kidney function is correspondingly high. In the nonclinical stage, sponsors need to characterize a candidate's pharmacology and tolerability well enough to support a go/no-go decision and the design of first-in-human studies. A well-chosen animal model generates reproducible data for that decision. Results in animal models inform, but do not by themselves establish, efficacy or safety in patients.

The main types of CKD models

The CKD models used in nonclinical studies fall into three broad groups: chemically induced models, in which a nephrotoxic agent such as adenine is administered; surgical (nephron-reduction) models, in which functioning kidney mass is removed or infarcted; and immunologic models, in which nephritis is induced by administering a specific antibody.^{[S4][S6][S7][S8]}

Each model has strengths and limitations, so the choice should follow from the research question and the endpoints to be measured. Matching the model to the mechanism, and building an evaluation panel that can detect the expected effect, is what makes a nonclinical CKD study informative.

Adenine-induced CKD model: features and induction

In the adenine model, kidney failure is induced by oral administration of adenine, a purine base. Adenine is metabolized to 2,8-dihydroxyadenine, which precipitates as crystals in the renal tubules. The crystal deposits cause tubular obstruction, tubulointerstitial inflammation, and fibrosis, leading to a progressive loss of renal function.^[S4][S5]

The adenine model avoids surgery and has been reported in both mice and rats.^[S4][S5]

Induction procedure and conditions

Adenine can be administered either mixed into the diet or by oral gavage. The mouse protocols cited in this article used dietary administration.^[S15]

• Dietary administration: adenine is mixed into standard chow. Exposure varies with food intake.
• Oral gavage: adenine is delivered directly into the stomach by gavage needle. The administered dose can be set per animal, but repeated handling is required.

Mice (commonly C57BL/6J) or rats at around 8 weeks of age are typically used, with an administration period of several weeks set according to the study objective.^[S4][S5]

Adenine concentration and disease severity in mice

The adenine concentration in the diet strongly influences how fast and how severely the disease develops. Understanding the differences between concentrations is essential for setting conditions that fit the study objective.^[S15]

The following are commonly reported conditions for mice.

0.15% adenine diet

A 0.15% adenine diet for 20 weeks has been reported in 8-week-old male C57BL/6 mice and produced CKD with reno-cardiac features.^[S15]

0.2% adenine diet

At 0.2%, BUN and creatinine rise sharply soon after the diet starts and body weight falls markedly. Because the disease progresses quickly, the timing of efficacy assessments needs care. Published mouse protocols therefore often use a short induction phase followed by a lower maintenance concentration: in one reported model, mice received 0.3% adenine for an induction period and were then maintained on 0.15% to 0.2%, and lowering the diet from 0.2% to 0.15% was followed by a decline in urea levels and stabilization of body weight.^[S15] A 0.2% diet for 4 weeks has also been reported to produce renal changes in mice similar to those in rats without mortality.^[S15]

Reported 0.15% protocols vary by strain and duration; select the concentration for the study objective and confirm the phenotype before test-article dosing.^[S15]

Surgical models: renal artery branch ligation and nephrectomy

5/6 nephrectomy: renal-infarction method

In the renal-infarction form of the 5/6 nephrectomy model, one kidney is removed and segmental arteries to the remaining kidney are ligated to infarct approximately two-thirds of it.^[S6] Reducing the number of functioning nephrons in this way induces chronic renal failure.^[S6] Rats are the usual species.^[S6]

Phenotype and severity depend on the extent of infarction, the rat strain, and the protocol.^[S6] Confirm the expected time course for the exact protocol before scheduling test-article dosing and assessments.

Comparison of renal-infarction and surgical-resection 5/6 nephrectomy models

The surgical-resection method removes one kidney and resects most of the remaining kidney mass, reproducing advanced loss of renal function.^[S6] The phenotype can be severe, with a risk of marked deterioration in general condition and increased mortality during the study, so the design needs care.^[S6]

The renal-infarction and surgical-resection methods are two forms of the 5/6 nephrectomy model and have distinct phenotypes: a comparative review reports more rapid, moderate-to-severe hypertension in the infarction model, and early normotension followed by mild-to-moderate hypertension in the resection model.^[S6] The choice between the two should depend on the research objective and the phenotype required.

Immunologically induced nephritis models

When the goal is to reproduce immune-mediated nephritis such as glomerulonephritis rather than nephron loss or toxic injury, models induced by administering a specific antibody are used. Two commonly described antibody-induced models are anti-GBM and anti-Thy-1 nephritis.^[S7][S8]

Anti-GBM antibody nephritis model

This model uses an antibody directed against the glomerular basement membrane (GBM), the filtration barrier of the glomerulus. Disease develops rapidly, and the model is commonly used to reproduce severe, rapidly progressive glomerulonephritis with crescent formation.^[S7]

Anti-Thy-1 antibody nephritis model

This model targets the mesangial cells that support the glomerular capillaries. It reproduces mesangial proliferative glomerulonephritis, with histologic features similar to those seen in human IgA nephropathy, and it is distinctive in that the lesions resolve spontaneously, allowing the recovery phase to be studied.^[S8]

Even within the single label "CKD," the appropriate model differs according to the mechanism of action being targeted and the site of immune injury of interest.

Efficacy endpoints and practical points for running CKD studies

Rather than relying on a single readout, prespecify a panel of endpoints covering renal function, urinary findings, and histopathology, and justify each one for the model and the mechanism being studied. Categories to consider:

• Blood chemistry: BUN, serum creatinine, cystatin C
• Urinalysis: urinary protein, N-acetyl-β-D-glucosaminidase (NAG), urine volume
• Histopathology: glomerular basement membrane thickening, tubular dilation, interstitial fibrosis, crescent formation
• Other: kidney weight and special stains (H&E, PAS, Masson's trichrome)

Prespecify assessment timing based on the documented disease time course of the selected model, and justify when induction, test-article dosing, and serial measurements occur.

A CRO engagement may include scoping, protocol design, contracting (often a master services agreement with a study-specific work order), Institutional Animal Care and Use Committee (IACUC) review, model induction, dosing, and reporting. Ask the CRO for its actual sequence and timeline, including when IACUC review takes place and how it affects scheduling. Coming to the first discussion with a clear statement of the candidate's mechanism of action makes model selection and scheduling faster.

Improving the translational value of nonclinical CKD studies

Biomarkers that detect injury and drug effects earlier

Renal function in nonclinical studies has traditionally been assessed by serum BUN and creatinine together with histopathology. Urinary injury biomarkers have been evaluated for voluntary use alongside these standard endpoints in rat nephrotoxicity studies.^[S9]

Candidate biomarkers include kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), liver-type fatty acid-binding protein (L-FABP), and cystatin C. FDA's 2008 qualification applied to KIM-1, albumin, total protein, β2-microglobulin, cystatin C, clusterin, and trefoil factor-3 (TFF3) for voluntary use with standard endpoints in rat nephrotoxicity studies.^[S9]

Modeling common CKD comorbidities

Diabetes and hypertension are common causes or comorbidities of CKD in US adults.^[S1][S2] Comorbidity models are used to reflect that context, including the interaction between kidney disease and cardiovascular disease (cardiorenal syndrome).

Alongside the simpler surgical and chemical models, there is growing demand for models that mimic this complex background, such as the ZSF1 rat, an obese, type 2 diabetic strain that develops nephropathy,^[S10] and streptozotocin (STZ)-induced diabetic nephropathy models.^[S11] Selecting a model that resembles the intended patient population can improve the translational relevance of the nonclinical package. It does not, by itself, predict the outcome of clinical trials.

Bridging species differences: microphysiological systems and imaging

Animal models remain central to nonclinical CKD research, although since the FDA Modernization Act 2.0 of 2022 they are no longer a statutory prerequisite for an IND in the United States.^[S3] Species differences in renal anatomy, the pace of fibrosis, and immune responses limit how far rodent findings can be extrapolated. Human iPSC-derived kidney organoids^[S12] and glomerulus-on-a-chip systems^[S13] have been reported as examples of microphysiological systems (MPS) that may complement animal studies.

In vivo, BOLD (blood oxygen level-dependent) MRI has been used to assess renal oxygenation in patients with CKD and in 5/6 nephrectomy/infarction rats.^[S14] Whether a CRO offers imaging endpoints of this kind is a reasonable item to include when comparing providers.

Summary

CKD models include chemically induced models such as the adenine model, surgical models such as the renal-infarction and surgical-resection forms of 5/6 nephrectomy, and immunologic models such as anti-GBM and anti-Thy-1 nephritis.^{[S4][S6][S7][S8]} Because their induction methods and phenotypes differ, the model should be chosen to fit the research objective and the endpoints.

If you are planning a nonclinical study in CKD, discuss model selection and endpoint design with a CRO that runs these models routinely. Our directory of US nonclinical CROs indicates which providers list renal disease models among their services, together with the sources for each entry.